1. Field of the Invention
The present invention relates to a semiconductor composite device, a method for manufacturing the semiconductor composite device, an LED head that employs the semiconductor composite device, and an image forming apparatus that employs the LED head.
2. Description of the Related Art
FIG. 11 is a perspective view of a conventional light-emitting diode (LED) unit 2000 on which LED chips are mounted.
FIG. 12 is a top view illustrating a part of an LED chip 2001.
FIG. 13 is a cross-sectional view taken along a line A-A of FIG. 12.
Referring to FIG. 11, the LED unit 2000 includes primarily a plurality of LED chips 2001, a plurality of driver IC chips 2002, wires 2003 that connect between the LED chips 2001 and driver IC chips 2002, and a unit substrate 2005. Referring to FIG. 12, the LED chip 2001 includes light emitting elements 2101, electrodes 2102 for light-emitting elements 2101, and electrode pads 2103 for wiring. The electrode pads 2103 should have a sufficient area for reliable gold-wire bonding. Therefore, the pad size is selected to be about 100×100 μm. The cost of a chip is determined by the number of chips produced from a sheet of semiconductor wafer. Thus, a small chip width is a key factor. There exists a need for a semiconductor device such as an LED chip and an IC chip where pads take up only a small area and wire bonding is not required. One way of solving the aforementioned problems is that a semiconductor thin film is bonded onto an Si-substrate in which driver ICs are formed for controllably driving light-emitting elements and the semiconductor thin film is electrically connected to the driver ICs by means of metal wires. In this case, a critical point is the way in which the semiconductor thin film is bonded onto a substrate which is a different type from the semiconductor thin film.
For a type in which the light-emitting chips are bonded to an Si-substrate on which driver ICs are fabricated, a semiconductor thin film may be conveniently bonded to a metal layer formed on the Si-substrate. For a type where a semiconductor thin film is bonded to a substrate of a different type from the thin film semiconductor, a bonding method may be conveniently employed which utilizes Van der Waals forces that act between atoms or molecules of the semiconductor thin film and the substrate of the different type from the thin film semiconductor. However, for bonding based on the Van der Waals forces, surfaces of the semiconductor thin film and substrate are made hydrophilic and are then placed together so that the surfaces are bonded to each other due to hydrogen bonding. However, metal surfaces are often hydrophobic and therefore it has not been known what type of surface type is the most appropriate.